1. Field of the Invention
The present invention generally relates to magnetic disk drives and magnetic head carriage assemblies, and more particularly, to a magnetic disk drive and a magnetic head carriage assembly suitable for high-density recording.
2. Description of the Related Art
At present, high-density recording is being introduced to 3.5-inch and other types of magnetic disk drives. In order to increase the recording density, however, it is necessary to increase the number of tracks per unit length of magnetic disk, or TPI, and increasing TPI decreases the width of each track and requires a consequent enhancement in the accuracy with which the magnetic head is positioned. Increasing the TPI to 25,000, for example, reduces the track pitch to 1 xcexcm, requiring the positional accuracy of the magnetic head to be within 0.1 xcexcm. Also, there is a trend toward smaller magnetic disk drives and less power consumption. Therefore, it is necessary to develop a magnetic head carriage assembly which satisfies such demands.
To improve the positioning accuracy of the magnetic head, the loop gain of a positioning servo system should be increased, and the crossover frequency of the open loop should be increased. The maximum loop gain of the positioning servo system is determined by the natural frequency of the head carriage which is rotationally supported on a shaft. Therefore, in a conventional magnetic disk drive, the head carriage has a high rigidity so as to increase the natural frequency of the head carriage, and to increase the loop gain of the positioning servo system as much as possible.
However, even if the head carriage has a high rigidity, a translational force acts on the bearing in such a direction that influences the positioning of the magnetic head. In such a case, it is difficult to obtain the positioning accuracy of the magnetic head of 0.1 xcexcm or less.
A general object of the present invention is to provide a head carriage assembly in which the above disadvantages are eliminated.
The above object of the present invention is achieved by a head carriage assembly which comprises: a head carriage which has a hub portion rotatably supported about a rotational center shaft on a base, and moves a head in a radial direction of a rotating disk; a first driving unit which generates a force to rotate the head carriage; and a second driving unit which generates a force to rotate the head carriage in a direction perpendicular to a line connecting a rotational center of the head carriage and the head. The second driving unit comprises: a coil secured outside the hub portion of the head carriage, and has an axial line vertical to a surface which includes the rotational center shaft on the base; and a magnetic circuit body which is made up of a yoke and a permanent magnet, with a magnetic gap being formed between the yoke and the permanent magnet, and engages the coil to be secured to the base. A part of the coil moves within the magnetic gap.
Since the axial line of the coil is perpendicular to the surface including the rotational center shaft, the space for the coil in the circumferential direction of a circle around the rotational center shaft does not have to be large. When the head carriage is rotated so that the head moves in the radial direction of the disk, the coil does not require a large space for moving in the circumferential direction. Accordingly, the magnetic circuit body can be small in the circumferential direction. Here, it is possible to place the coil outside the hub portion of the head carriage in the limited space. The coil can be situated at a longer distance from the rotational center shaft compared with the prior art, and the torque constant of the driving unit can be larger than in the prior art. Thus, the magnetic circuit body can be made smaller, and power consumption can be reduced compared with the prior art.
The object of the present invention is also achieved by a disk drive provided with the above head carriage assembly.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.